1. Field of the Invention
The invention relates to an apparatus that controls the boost pressure of an internal combustion engine, and a boost pressure control method.
2. Description of the Related Art
There is a known technology that improves the responsiveness of a turbocharger by increasing the exhaust temperature, that is, the energy of exhaust, through retardation of the ignition timing or retardation of the fuel injection timing, or the like (e.g., see Japanese Examined Patent Application Publication No. HEI 7-101011).
Herein, if the thermal energy of exhaust is increased through retardation of the ignition timing or retardation of the injection timing, or the like, the torque generated by the internal combustion engine correspondingly decreases. Specifically, assuming that the intake air amount is fixed, the net torque becomes smaller if the thermal energy of exhaust is increased than if it is not increased. This is because if the thermal energy of exhaust is increased by retardation of the ignition timing or the like, the boost pressure in the next and later cycle rises, but the torque generated in the present cycle decreases. Even in the case where the responsiveness of boost pressure is enhanced by increasing the energy of exhaust, the drivability deteriorates if the enhancement of the boost pressure responsiveness is surpassed by the decline in the responsiveness of engine rotation speed caused by a decline in the generated torque.
Besides, during rapid acceleration or the like, the generated torque is declined by retarding the ignition timing in order to reduce the shock or the like. In this case, if the retardation of the ignition timing or the like is performed as a means for increasing the energy of exhaust, its effect of preventing decline in drivability is small.